This invention relates to tools for the reworking of valve guides in cylinder heads for internal combustion engines, and more particularly, to both a fixture for guiding the reworking operations on valve guides and a boring tool used with such fixtures.
In the past, valve guide reworking operations have been accomplished by using either large and immovable machines requiring the precise mounting of cylinder heads on the machine at an angle in order to produce the proper reworking alignment, or smaller tools which could be mounted on the cylinder head. The large machines typically include a heavy base on which is mounted a drill press or other boring tool, thus necessitating the mounting of the cylinder head in a precise position to provide the proper alignment with the drill press. The cylinder head mounting on these machines is a tedious operation and one which, of necessity, must be repeated for each valve guide since the intake and exhaust valve guides in modern engines are often formed at opposing angles.
The smaller tools, which could be mounted on the cylinder head when the cylinder head was in any position, are based on alignment principles, which often produce inaccurate results. One smaller tool utilized the principle of aligning the guide tool with the valve guide bore by means of the valve spring seat on the side of the cylinder head opposite the valve seat. However, valve spring seats are normally not concentrically located with respect to the valve guide bore, thus causing this method to be inaccurate. Other small tools for the reworking operations necessitate a mounting guide fixture on the cylinder head by means of one of the many holes provided in the cylinder head to mount the head on the engine block. However, if the mounting hole was in any way deformed or displaced, the capability of aligning the tool properly was thereby reduced.
To overcome the above problems, a valve guide boring fixture was designed that allows a worker to quickly and easily align a boring guide with the central axis of the valve to ensure proper alignment. This valve guide boring fixture is described in commonly-assigned U.S. Pat. No. 5,281,057. This valve guide boring fixture is designed for use with a small, easily movable boring tool so as not to require movement of the cylinder head.
One problem associated with such smaller tools, however, is that they typically take the form of a hand drill having a general "L" shape whereby the palm of the user's hand is required to be facing downward when the drill is used to ream a vertically oriented bore. Such hand drills are thereby of relatively poor ergonomic design, since a worker utilizing such a tool may develop carpal tunnel syndrome through excessive, repetitive motions in using such hand tools.
Further problems relating to safety issues arise in the use of such tools, since there are many potential pinch points where a worker may be required to place his or her fingers during operation of the tool. Further still, the reliance of such prior art arrangements upon the operator's ability to feed the reaming shaft to the proper depth and at the proper speed, introduces inconsistent results. Also, the fatigue caused through the use of these tools can effect the accuracy of the reaming.